1. Field of the Invention
The present invention relates to a manufacture method for photovoltaic module.
2. Description of the Prior Art
A photovoltaic module has a construction wherein a plurality of solar cells are connected in series and/or in parallel by means of wiring members electrically connected to positive and negative electrodes thereof. In the manufacture of the photovoltaic module, the conventional practice is to use solder for connecting the electrodes of the solar cells with the wiring members. The solder is widely used because of its excellent connection reliability including conductivity, bonding strength and the like.
From an environmental standpoint and the like, on the other hand, the solar cells also employ a wiring connection method not relying on the solder. There is known a method, for example, which uses a conductive adhesive film to interconnect the solar cells and the wiring material. Such a method is disclosed in, for example, U.S. Patent Publication No. 2009/0288697A1.
As shown in FIG. 11, a connection structure using the conductive adhesive film is arranged such that an electrode 21, 22 of a solar cell 20, a conductive adhesive film 10 and a wiring material 30 are laminated on top of each other in this order. The conductive adhesive film 10 used herein comprises conductive particles 1 and a thermosetting resin adhesive component 2, as shown in FIG. 12.
The conductive adhesive film 10 is used for allowing the wiring material 30 to interconnect the electrodes 21, 22 of adjoining solar cells 20, 20 in series and/or in parallel.
An inventive method which uses the conductive adhesive film to interconnect the electrode of the solar cell and the wiring material is described with reference to FIG. 13 to FIG. 16. FIG. 13 is a schematic diagram showing a step in which the conductive adhesive film is pasted on the electrode of the solar cell. FIG. 14 is a schematic diagram showing a step of temporarily pressure bonding the wiring material to the solar cells. FIG. 15 is a schematic diagram showing a step of permanently pressure bonding the wiring material to the solar cell. FIG. 16 is a schematic diagram showing the wiring material fixed to the electrode of the solar cell.
First, as shown in FIG. 13, the conductive adhesive films 10, 10 are pasted on the electrodes 21, 22 of the solar cell 20. Subsequently, as shown in FIG. 14, the wiring material 30, 30 are respectively placed on upper and lower sides of the solar cell 20 having the conductive adhesive films 10, 10 pasted thereon and temporarily pressure bonded to the solar cell. The temporary pressure bonding is performed as follows. Heater blocks 40, 40 are pressed down on the solar cell at a low pressure of about 0.2 MPa, for example, so as to press the wiring material 30 against the solar cell 20. The temperature of the heater blocks 40, 40 is raised to about 90° C., for example, to provide low-temperature heating in which the resin adhesive component is not thermally set. The wiring materials 30, 30 are temporarily pressure bonded to the solar cell 20 by the low-temperature heating. Thus, the solar cells 20, 20 are set in array.
Next, the operation proceeds to a step of permanently pressure bonding the wiring material 30. As shown in FIG. 15, the arrayed solar cells 20, 20 having the wiring material 30 attached thereto are pressed by the heater blocks 40, 40 under high temperature, high pressure conditions. The heater temperature is higher than a temperature at which the resin adhesive component is thermally set, namely 120° C. or above for example. The pressure is as high as 2 MPa. The wiring material 30 is pressed against the solar cell 20 while the resin adhesive component is thermally set so that the electrode 21, 22 of the solar cell 20 is connected with the wiring material 30. Thus, a string of solar cells is formed as shown in FIG. 16.
Next, the string of solar cells thus fabricated is subjected to an inspection step in which the solar cell string is visually inspected to check for appearance and wiring so as to reject any defective solar cells. The photovoltaic module is formed using non-defective strings.
In the above manufacture process, the defective parts are mainly produced in the permanent pressure bonding step in which the solar cells are prone to fracture or cracks attributable to the pressure bonding. The production of a inferior part dictates the need to perform a repair work. The repair work is described with reference to FIG. 17A to FIG. 18C. FIG. 17A is a schematic diagram showing the repair work for defective solar cell or a state where a defective solar cell exists. FIG. 17B is a schematic diagram showing a state where the defective solar cell is removed. FIG. 18A is a schematic diagram showing a state where the defective solar cell exists. FIG. 18B is a schematic diagram showing a state where the defective solar cell is removed. FIG. 18C is a schematic diagram showing a state where the repair work for the defective solar cell is completed.
As shown in FIG. 17A to FIG. 18C, only a solar cell 20a suffering a facture or crack (20b) detected in the inspection step is removed and a new solar cell 20r is mounted in the vacant place. In the example shown in FIG. 17A, the central solar cell 20a includes the facture or crack (20b) and hence, an operation for removing the defective solar cell 20a is required.
However, a problem exists in a case where the conductive adhesive film 10 is used. Bonding strength between the thermally set resin adhesive component and the solar cell 20 is so strong that the wiring material 30 cannot be separated without being seriously deformed. If the fractured solar cell 20a is separated, as shown in FIG. 17B, the wiring material 30 may be deformed or a part of the thermally set resin adhesive component of the conductive adhesive film 10 or of the solar cell may stick to the wiring material 20. This makes it difficult to reuse the wiring material 30.
Hence, the repair work may be performed as shown in FIG. 18A to FIG. 18C. First, the solar cell 20a suffering the facture or crack (20b) detected in the inspection step is cut off from the string, as shown in FIG. 18A. For this purpose, the wiring materials 30, 30 on the fractured solar cell 20a are individually cut off at forward place (arrow A in the figure) and at rearward place (arrow B in the figure) on the lower side thereof as seen in the figure. After cutting off the wiring materials 30, 30, the fractured solar cell 20b with the wiring material 30 is bodily removed (see FIG. 18B). As shown in FIG. 18B, the wiring material 30 on the lower side of the forward solar cell 20 is severed at an end thereof. The wiring material 30 on the upper side of the rearward solar cell 20 is severed in the vicinity of an end of the forward solar cell 20.
Subsequently, a solar cell for repair 20r is prepared which has the wiring materials 30, 30 pressure bonded to the electrodes 21, 22 thereof by using the conductive adhesive film. In this example, the wiring material 30 on the upper side of the solar cell for repair 20r has a length to reach the wiring material 30 on the forward solar cell 20. The wiring material 30 on the lower side of the solar cell 20r is fixed to the solar cell 20r over a length sufficient for connection with the wiring material 30 extending from the upper side of the rearward solar cell 20.
As shown in FIG. 18C, the wiring material 30 of the solar cell for repair 20r and each corresponding one of the wiring materials 30, 30 of the string are interconnected at place (arrow C in the figure) by soldering. The repair work is completed by replacing the defective solar cell 20a with the non-defective solar cell 20r in this manner.
As described above, the wiring material cannot be reused because the bonding strength between the thermally set resin adhesive component of the conductive adhesive film and the solar cell is so strong. Accordingly, the repair work includes the steps of cutting off the wiring materials at the opposite ends of the solar cell suffering the fracture or crack, and soldering the wiring materials pressure bonded to the non-defective solar cell. This results in the decrease of throughput.
Further, the above-described repair method involves another problem that the soldered connection applies heat to the thermally set resin adhesive component of the non-defective solar cell, which is decreased in the bond strength to the wiring material.